1. Field of the Invention
The present invention relates to an electron beam based inspection apparatus for inspecting defects in patterns formed on the surface of an object to be inspected, and more particularly, to an inspection apparatus useful, for example, in inspecting defects on a wafer in a semiconductor manufacturing process, which includes irradiating an object to be inspected with an electron beam, detecting secondary electrons which vary in accordance with the properties of the surface thereof to form image data, and inspecting patterns formed on the surface of the object to be inspected based on the image data at a high throughput, and a method of manufacturing devices at a high yield rate using the inspection apparatus. More specifically, the invention relates to a projection type electron beam inspection apparatus which adopts a area beam and a method of manufacturing devices using the inspection apparatus.
2. Field of the Invention
In semiconductor processes, design rules are reaching 100 nm and the method of production form is evolving from mass production, with a few models, such as a DRAM, into small-lot production with a variety of models such as a SOC (Silicon on chip). This has resulted in an increase in the number of processes, and an improvement in yield for each process is essential; which makes it more important to inspect for defects occurring in each process. The present invention relates to an apparatus to be used in the inspection of a wafer after particular steps in the semiconductor fabrication process, and in particular to an inspection method and apparatus using an electron beam and also to a device manufacturing method using the same.
3. Description of the Related Art and Problems to be Solved by the Invention
4. Description of the Prior Art
In conjunction with a high level of integration of semiconductor devices and a micro-fabrication of patterns thereof, an inspection apparatus with higher resolution and throughput is desired. In order to inspect a wafer substrate with 100 nm design rules for any defects, a resolution equal to or finer than 100 nm is required, and the increased number of processes resulting from large-scale integration of devices calls for an increase in the number of inspections, which consequently requires higher throughput. In addition, as multilayer fabrication of devices has advanced, the apparatus is further required to have a function for detecting contact failures in vias for interconnecting wiring between layers (i.e., electrical defects). In the current trend, an inspection apparatus using optical methods has been typically used, but it is expected that an inspection apparatus using an electron beam may soon enter the mainstream, substituting for inspection apparatus using optical methods, given the requirements of higher resolution and detection of contact failures. The electron beam method, however, has a weak point in that it is inferior to the optical method in throughput.
Accordingly, it is desirable to have an apparatus having higher resolution and throughput and being capable of detecting the electrical defects. It has been known that the resolution of the optical method is limited to ½ of the wavelength of the light to be used, and it is about 0.2 .mu.m in a typical case of visible light being put to practical use.
On the other hand, in the method using an electron beam, typically a scanning electron microscopy method (SEM method) has been put to use, wherein the resolution thereof is 0.1 .mu.m and the inspection time is 8 hours per wafer (20 cm wafer). The electron beam method has the distinctive feature that it is able to inspect for any electrical defects (breaking of wires in the wirings, bad continuity, bad continuity of via). However, the inspection speed (sometimes also referred to as inspection rate) thereof is very low, and so the development of an inspection apparatus with higher inspection speed has been eagerly anticipated.
Generally, since an inspection apparatus is expensive and the throughput thereof is rather lower as compared to other processing apparatuses, the inspection apparatus has been used after an important process, for example, after the process of etching, film deposition, CMP (Chemical-mechanical polishing) flattening or the like.
The scanning method (SEM) using an electron beam will now be described. In the inspection apparatus of SEM method, the electron beam is contracted to be finer (the diameter of this beam corresponds to the resolution thereof) and this fined beam is used to scan a sample so as to irradiate it linearly. On the other hand, moving a stage in the direction normal to the scanning direction allows an observation region to be irradiated by the electron beam as a plane area. The scanning width of the electron beam is typically some 100 .mu.m. Secondary electrons emanating from the sample by the irradiation of said contracted and fined electron beam (referred to as a primary electron beam) are detected by a detector, either a scintillator plus photo-multiplier (i.e., photoelectron multiplier tube) or a detector of semiconductor type (i.e., a PIN diode) or the like. The coordinates for the irradiated locations and an amount of the secondary electrons (signal intensity) are combined and formed into an image, which is stored in some recording medium or displayed on a CRT (a cathode ray tube). The above description illustrates the principles of the SEM (scanning electron microscopy), and defects in a semiconductor wafer (typically made of Si) in the course of processes may be detected from the image obtained in this method. The inspection rate (corresponding to the throughput) is varied depending on the amount (the current value), beam diameter, and speed of response of the primary electron beam. A beam diameter of 0.1 .mu.m (which may be considered to be equivalent to the resolution), a current of 100 nA, and a detector speed of 100 MHz are currently the highest values, and in using those values the inspection rate has been about 8 hours for one wafer having a diameter of 20 cm. This inspection rate, which is extremely low compared to the optical method (not greater than 1/20), has been a serious production problem (drawback).
Also, in regard to the prior art of inspection apparatus related to the present invention, an apparatus using a scanning electron microscope (SEM) has been commercially available. This apparatus involves scanning an object to be inspected with a fine electron beam at very narrow intervals of scanning width, detecting secondary electrons emitted from the object to form a SEM image, and comparing such SEM images of different dies at the same locations to extract defects of the object being inspected.
Conventionally, however, there has been no electron beam based defect inspection apparatus which is completed as a general system.
A defect inspection apparatus which applies SEM requires a long time for defect inspection. In addition, increasing the beam current to improve throughput would cause a degradation of the beam due to the space-charge effect and charging on the wafer with insulating material formed on the surface thereof, thereby failing to produce satisfactory SEM images.
Hitherto, no proposal has been made for the overall structure of an inspection apparatus which takes into account the combination of an electron-optical device for irradiating an object to be inspected with an electron beam, with other subsystems associated therewith for postioning the object to be inspected to for irradiating by the electron-optical device in a clean state, and for aligning the object to be inspected. Further, with the trend of increasing diameters of wafers to be subjected to inspection, the subsystems are also required to cope with wafers of such large diameters.
In view of the problems mentioned above, it is an object of the present invention to provide an inspection apparatus which employs an electron beam based electron-optical system, and achieves harmonization of the electron-optical system with other components, which constitute the inspection apparatus, to improve the throughput.
It is another object of the present invention to provide an inspection apparatus which is capable of efficiently and accurately inspecting an object by improving a loader for carrying the object to be inspected between a cassette for storing objects under inspecting and a stage device for aligning the object to be inspected with respect to the electron-optical system, and devices associated with the loader.
It is a further object of the present invention to provide an inspection apparatus which is capable of solving the problem of charging, experienced in the SEM, to accurately inspect an object.
It is a further object of the present invention to provide a method of manufacturing devices at a high yield rate by inspecting an object such as a wafer, using the inspection apparatus as mentioned above.
Also, with increasing integration of semiconductors, there has been a need for a sensitive inspection apparatus to be used in the semiconductor device manufacturing process for defect inspection in the pattern or the likes in semiconductor wafers. In this regard, there have been electron microscopes used as the inspection apparatus for such defect inspections, as disclosed in Japanese Patent Laid-open Publications Nos. Hei 2-142045 and Hei 5-258703.
For example, in the electron microscope as disclosed in Japanese Patent Laid-open Publication No. Hei 2-142045, an electron beam emitted from an electron gun is converged by an objective lens to irradiatea sample to be inspected, and secondary electrons emitted from the sample are detected by a secondary electron detector. In addition, in this electron microscope, a negative voltage is applied to the sample, and further an E.times.B type filter is arranged between the sample and the secondary electron detector, said filter having an electric field and a magnetic field crossed at right angles.
With such a configuration, this electron microscope allows a high resolution to be obtained by decelerating the electrons irradiated onto the sample by way of the negative voltage applied to the sample.
Further, the application of the negative voltage to the sample helps accelerate the secondary electrons emitted from the sample, and the accelerated secondary electrons are further deflected by the E.times.B type filter toward the secondary electron detector, thus to be efficiently detected by the secondary electron detector.
In those conventional apparatuses using the electron microscope as described above, the electron beam from the electron gun is kept accelerated to be highly energized until just before it impinges onto the sample, by a lens system such as an objective lens with a high voltage applied. Then, the negative voltage applied to the sample decelerates electrons impinging upon the sample, thus allowing a high resolution to be achieved.
However, since the high voltage is applied to the objective lens, while the negative voltage is applied to the sample, there has been a risk that an electric discharge may occur between the objective lens and the sample.
Further, in the electron microscope in the prior art, even in the case where no negative voltage is applied to the sample, if there is a great potential difference between the objective lens and the sample, then it is again feared that the electric discharge may occur between the objective lens and the sample.
Still further, if the voltage applied to the objective lens is set lower in order to deal with a possible electric discharge to the sample, the electrons aren't sufficiently energized, resulting in a poor resolution.
An explanation will be further given for a case where the sample to be inspected is a semiconductor wafer having a via, that is a wiring pattern extending in the approximately vertical direction to the upper-layer and lower-layer wiring planes for providing an electrical connection between the upper layer wiring and the lower layer wiring.
When the semiconductor wafer with the via is inspected for defects by using a conventional electron microscope, a high voltage, for example, a voltage of 10 kV is applied to the objective lens as in the above description. Further, in this case, it is assumed that the semiconductor wafer is grounded. Accordingly, an electric field is generated between the semiconductor wafer and the objective lens.
These conditions could make the electric field more intense in the vicinity of the via on the surface of the semiconductor wafer, thus forming a high electric field. Then, when the electron beam is irradiated onto the via, a large number of secondary electrons is emitted from the via, which is further accelerated by the high electric field in the vicinity of the via. Those accelerated secondary electrons have a sufficient energy (>3 eV) to ionize a residual gas generated by the irradiation of the electron beam onto the semiconductor wafer. Accordingly, the secondary electrons ionize the residual gas so as to generate ionized charged particles.
Then, said ionized charged particles, i.e., the positive ions, are accelerated by the high electric field in the vicinity of the via toward the via to impinge against the via, so that more secondary electrons are emitted from the via. Through a series of these positive feedback, eventually an electric discharge occurs between the objective lens and the semiconductor wafer and damages the pattern or the like on the semiconductor wafer, which has been problematic in the prior art.
Thus, an object of the present invention is to provide an electron gun apparatus which can prevent an electric discharge to a sample being inspected and a method for manufacturing a device by using said electron gun apparatus.
Also, as stated above, an inspection for defects in a mask pattern used in manufacturing a semiconductor device or in a pattern formed on a semiconductor wafer has been performed by the steps of detecting secondary electrons emitted from a sample upon irradiation of a primary electron beam against a surface of the sample, obtaining a pattern image of the sample, and comparing said image with a reference image. Typically, such defect inspection apparatus has been equipped with an E.times.B separator for separating the primary electrons and the secondary electrons.
FIG. 52 shows schematically a typical configuration of a projective electron beam inspection apparatus having an E.times.B separator. An electron beam emitted from an electron gun 721 is formed to be rectangular in shape with a forming aperture (not shown) and reduced in size by the electrostatic lenses 722, thus to be a formed beam of 1.25 mm square at the center of an E.times.B separator 723. The formed beam is deflected by the E.times.B separator 723 so as to be normal to a sample W, and reduced to be ⅕ in size with an electrostatic lens 722, which is then irradiated against the sample W. A beam of the secondary electrons emitted from the sample W has a certain intensity corresponding to the pattern data on the sample W, which is expanded by the electrostatic lenses 724, 741, and then enters into a detector 761. The detector 761 generates an image signal corresponding to the intensity of the received secondary electrons, which is compared with a reference image, thereby detecting any defects in the sample.
The E.times.B separator 723 has a configuration in which an electric field and a magnetic field cross at right angles within a plane orthogonal to the normal of the surface of the sample W (the upward direction on paper), so that it advances the electrons straight forward when the relationship of the electric field, the magnetic field, and the energy and speed of the electrons meets certain criteria, while it deflects the electrons in any case other than the said case. In the inspection apparatus of FIG. 44, the conditions are set so that the secondary electrons are advanced straight ahead.
FIG. 53 shows more precisely the movements of the secondary electrons emitted from the rectangular area on the surface of the sample W, which has been exposed to the primary electron beam. The secondary electrons emitted from the sample surface are magnified with the electrostatic lens 724, and imaged onto a central area 723a of the E.times.B separator 723. Since the electric field and the magnetic field of the E.times.B separator 723 have been set such that the secondary electrons are allowed to be advanced straight ahead, the secondary electrons are thus advanced straight ahead to be magnified with the electrostatic lenses 741-1, 741-2 and 741-3, and then imaged on a target 761a within the detector 761. Then, the electron in the image is multiplied by MCP (Multi Channel Plate, not shown) and is formed into an image by a scintillator, CCD (Charge Coupled Device), or the like (not shown). Reference numerals 732 and 733 respectively designate aperture diaphragms arranged in a secondary optical system.
FIG. 54 shows a schematic configuration of a conventional E.times.B separator and the distribution of an electric field generated by said separator. A pair of parallel plate electrodes 723-1 and 723-2 is used to generate an electric field, and a pair of magnetic poles 723-3 and 723-4 is used to generate a magnetic field orthogonal to said electric field. In this configuration, since the magnetic poles 723-3 and 723-4 are made of metals having the ground potential, the electric field is forced to bend toward the ground sides. Accordingly, the distribution of the electric field is as shown in FIG. 54, and the parallel pattern of the electric field may only be obtained in the small central region.
In the case where an E.times.B separator having such a configuration as described above has been applied to a defect inspection apparatus such as a projective electron beam inspection apparatus, there has been a problem of efficiency in inspection in that the irradiated region of the electron beam cannot be enlarged, in order to perform a precise inspection.
Thus, an another object of the present invention is to provide an E.times.B separator which allows a region including both the electric field and the magnetic field having uniform intensities and cross at right angles to each other, to be expanded in a plane parallel to a sample, and which also allows the outer diameter of the whole body to be reduced. Further, another object of the present invention is to reduce the aberration for the detected image obtained, by means of said E.times.B separator applied to a defect inspection apparatus, thus to conduct the precise defect inspection efficiently.
Also, as stated above, there is a conventional apparatus which, in an inspection of a pattern on a semiconductor wafer or a photo mask with an electron beam, reveals a defect in the following way: primarily it scans the surface of a sample such as the semiconductor wafer or the photo mask, or it scans the sample, by sending the electron beam thereto; secondarily it detects secondary charged particles generated from the surface of said sample to generate image data based on the detected result; and lastly it compares the data per cell or die.
However, the above defect inspection apparatus in the prior art has been problematic in that the irradiation of the electron beam causes the surface of the sample to be charged, and carriers from this charging cause a distortion in the image data, which makes it difficult to detect any defects accurately. When alternatively the electron beam current is reduced to make the distortion by the carriers small enough to resolve the problem of said distortion in the image data, the S/N ratio for the secondary electron signal is adversely affected, so that the possibility of invalid error detection is increased, which has been another problem. Further, it has also been a problem in the prior art that multiple scanning and averaging processes for improving the S/N ratio causes a decrease in throughput.
Therefore, another object of the present invention is to provide an apparatus which prevents any distortion from being caused by charging, or which minimizes such distortions if any, and thereby allows a highly accurate defect inspection to be performed, and also to provide a method for manufacturing a device by using said apparatus.
Also, there has been known an apparatus for inspecting a substrate for any defects in an image formed on the substrate in such a manner that the apparatus irradiates a charged particle beam against a surface of the substrate to scan said surface by said charged particle beam, detects secondary electrons emanated from the surface of the substrate, generates image data from the detected result, and then compares the data for each die to one another to detect those defects.
However, this type of imaging apparatus according to the prior art, including the above-described apparatus that has been disclosed in the publication, has been problematic in that the potential distribution on the surface of the substrate or the object to be inspected is not necessarily uniform and the contrast of the image is insufficient, which may cause distortion.
Therefore, a further object of the present invention is to provide an imaging apparatus having an improved performance in defect detection without any loss of throughput.
Another object of the present invention is to provide an imaging apparatus having an improved performance in defect detection by improving the contrast in an image obtained by the detection of secondary electrons from the object to be inspected.
Still another object of the present invention is to provide an imaging apparatus having improved performance in defect detection by making uniform the potential distribution on the surface of an object to be inspected and thereby improving the contrast, thus reducing distortion, in an image obtained by the detection of secondary electrons from said surface of the object to be inspected.
Yet another object of the present invention is to provide a device manufacturing method in which a sample in the course of processes is evaluated by using such an imaging apparatus as described above.
There has also been one such prior art defect inspection apparatus used conventionally in a semiconductor manufacturing process or the like, which inspects a sample such as a wafer or the like for any defects by detecting secondary electrons emanated by irradiating a primary electron beam onto the sample.
Japanese patent Application Public Disclosure No. 11-132975, for example, discloses a defect inspection apparatus which comprises: an electron beam irradiating section for irradiating an electron beam against a sample; a projecting optical section for image-forming a one-dimensional and/or a two-dimensional image of secondary or reflected electrons, said secondary electrons being emanated in response to shape, material, and variation in potential on the surface of the sample; an electron beam detecting section for outputting a detection signal based on a formed image; an image display section for receiving said detection signal and displaying an electron image of the surface of the sample based thereon; and an electron beam deflecting section for changing the angle of incidence of the electron beam irradiated from the electron beam irradiating section onto the sample and the angle of intake of the secondary or reflected electrons into the projecting optical section. According to this inspection apparatus, the primary electron beam is irradiated onto a surface in a specified rectangular region of the sample wafer of the real device.
However, if the electron beam is irradiated on the surface in a relatively large area of the sample wafer of the real device, due to the sample surface being made of an insulating material such as silicon dioxide or silicon nitride, the electron beam irradiation against the sample surface and associated emanation of secondary electrons from the sample surface causes the sample surface to be positively charged, and an electric field produced by this potential has problematically caused a variety of image disorders in the secondary electron beam image.
The present invention has been made in the light of above-mentioned facts, and an object thereof is to provide an defect inspection apparatus and a defect inspection method that enable an inspection of a sample to be performed with higher accuracy by reducing positive charge builded-up in the surface of the sample, thereby overcoming the problem of disorder associated with this charge-up.
Another object of the present invention is to provide a semiconductor manufacturing method that can improve the yield of devices and prevent delivery of any defective products to market by using an inspection apparatus described above to carry out a defect inspection of a sample.
Further, a stage for accurately positioning a sample in a vacuum atmosphere has been used in an apparatus in which a charged particles beam such as an electron beam is irradiated onto the surface of a sample such as a semiconductor wafer so as to expose the surface of the sample to a pattern of a semiconductor circuit or the like, or so as to inspect a pattern formed on the surface of the sample, or in another apparatus in which the charged particles beam is irradiated onto the sample so as to apply an ultra-precise processing thereto.
When said stage is required to be positioned highly accurately, one structure has been conventionally employed, in which the stage is supported in non-contact manner by a hydrostatic bearing. In this case, the vacuum level in a vacuum chamber is maintained by forming a differential exhausting mechanism for exhausting a high pressure gas in an area of the hydrostatic bearing so that the high pressure gas supplied from the hydrostatic bearing may not be directly exhausted into the vacuum chamber.
FIG. 55 shows one of the examples of such a stage according to the prior art. In the configuration of FIG. 55, the tip portion of an optical column 71 or a charged particles beam irradiating section 72 of a charged particles beam apparatus for emitting and irradiating a charged particles beam against a sample is attached to a housing 98 which makes up a vacuum chamber C. The interior of the optical column is exhausted to vacuum through a vacuum pipe 710, as in the chamber C through a vacuum pipe 911. Herein, the charged particles beam is irradiated from the tip portion 72 of the optical column 71 against a sample W such as a wafer or the like placed thereunder.
The sample W is detachably held on a sample table 94, and the sample table 94 is mounted on the upper face of a Y directionally movable unit 95 of an XY stage (hereafter referred to as a stage for simplicity). The above Y directionally movable unit 95 is equipped with a plurality of hydrostatic bearings 90 attached on planes (on both of the right and left faces and also on a bottom face in FIG. 55[A]) facing to guide planes 96a of an X directionally movable unit 96 of the stage 93, and is allowed to move in the Y direction (lateral direction in FIG. 55[B]) with a micro gap maintained between the guide planes and itself by said hydrostatic bearings 90. Further, a differential exhausting mechanism is provided surrounding the hydrostatic bearing so that a high-pressure gas supplied to the hydrostatic bearing does not leak into the vacuum chamber C. This is shown in FIG. 56. Doubled grooves 918 and 917 are formed surrounding the hydrostatic bearings 90, and are regularly exhausted to vacuum through a vacuum pipe by a vacuum pump (not shown). Owing to such structure, the Y directionally movable unit 95 is allowed to move freely in the Y direction in the vacuum atmosphere as supported in the non-contact manner. Those doubled grooves 918 and 917 are formed in a plane of the movable unit 95 in which the hydrostatic bearing 90 is arranged, so as to circumscribe said hydrostatic bearing. The structure of the hydrostatic bearing may be any of those conventionally known and its detailed explanation can be omitted here.
The X directionally movable unit 96 having said Y directionally movable unit 95 loaded thereon is formed to be concave in shape with the top face opened, as obviously seen from FIG. 55, and said X directionally movable unit 95 is also provided with completely similar hydrostatic bearings and grooves, and further the unit 96 is supported in a non-contact manner with respect to the stage 97 so as to be movable freely in the X direction.
Combining said Y directionally movable unit 95 with the X directionally movable unit 96 allows the sample W to be moved to a desired position in the horizontal direction relative to the tip portion of the optical column or the charged particles beam irradiating section 72, so that the charged particles beam can be irradiated to a desired location of the sample.
With the stage including a combination of the hydrostatic bearing and the differential exhausting mechanism as described above, the guide plane 96a or 97a facing the hydrostatic bearing 90 makes a reciprocating motion between a high-pressure atmosphere in the electrostatic bearing portion and a vacuum environment within the chamber while the stage moves. During this reciprocating motion, such gas supply cycle is repeated in which while the guide plane is exposed to the high-pressure atmosphere, the gas is adsorbed onto the guide plane, and upon being exposed to the vacuum environment, the adsorbed gas is desorbed into the environment. Because of this gas supply cycle, every time when the stage moves, it has happened that the vacuum level in the chamber C is lowered, which has caused such problems that the exposure, inspection, or processing with the charged particles beam described above could not be carried out stably, and the sample might be contaminated.
Therefore, an another object of the present invention is to provide a charged particles beam apparatus capable of preventing the degradation of the vacuum level and thereby allow a process such as inspection or processing by a charged particles beam to be carried out stably.
Another object of the present invention is to provide a charged particles beam apparatus having a non-contact supporting mechanism by means of a hydrostatic bearing and a vacuum sealing mechanism by means of a differential exhausting so as to produce a pressure difference between the charged particles beam irradiating region and a supporting section of the hydrostatic bearing.
Still another object of the present invention is to provide a charged particles beam apparatus capable of reducing a gas desorbed from the surface of a part facing to the hydrostatic bearing.
Still another object of the present invention is to provide a defect inspection apparatus for inspecting the surface of a sample or an exposure apparatus for delineating a pattern on a surface of a sample, by using such a charged particles beam apparatus as described above.
Yet another object of the present invention is to provide a semiconductor manufacturing method for manufacturing a semiconductor device by using a charged particles beam apparatus such as described above.
Also, in the conventional stage including a combination of the hydrostatic bearing and the differential exhausting mechanism shown in FIG. 55, there have been such problems that because of the differential exhausting mechanism having been added, the structure has become more complicated and its reliability as a stage has decreased while its cost has increased over that of a stage having a hydrostatic bearing used in the atmospheric pressure.
Therefore, another object of the present invention is to provide a charged particles beam apparatus having a simple structure capable of being made compact without employing a differential exhausting mechanism for the XY stage.
Another object of the present invention is to provide a charged particles beam apparatus with a differential exhausting mechanism for exhausting a region on a surface of a sample to which a charged particles beam is to be irradiated, as well as for exhausting the inside of a housing containing an XY stage to vacuum.
Still another object of the present invention is to provide a defect inspection apparatus for inspecting the surface of a sample for defects or an exposing apparatus for delineating a pattern on the surface of the sample by using either of the charged particles beam apparatuses described above.
Yet another object of the present invention is to provide a method for manufacturing a semiconductor device by using either of the charged particles beam apparatuses described above.
Also, as stated above, there has been used in the semiconductor manufacturing processes or the like a defect inspection apparatus for inspecting a sample such as a semiconductor wafer for defects by detecting secondary electrons emitted upon an irradiation of a primary electrons against said sample.
In such defect inspection apparatus, there has been employed a technology in which an image recognition technique is put into practical use to accomplish an automated inspection and to achieve higher efficiency in the inspection. In this technology, a computer carries out a matching operation between pattern image data for a region to be inspected in the sample surface obtained by detecting the secondary electrons and reference image data for the sample surface stored in advance, so that it is automatically determined if there are any defects existing in the sample, based on the operation results.
Recently, especially in the semiconductor manufacturing field, patterns are increasingly miniaturized, and consequently requiring detection of finer defects with high precision and efficiency. Under such condition, even the defect inspection apparatus taking advantage of the image recognition technique described above must further improve its recognition accuracy.
However, there has been such a problem associated with the prior art described above, which is that a position mismatch occurs between the image of the secondary electron beam obtained upon irradiating the primary electron beam against the region to be inspected in the sample surface and the reference image prepared in advance, which decreases the accuracy in defect detection. This position mismatch becomes a serious problem especially when the irradiation region of the primary electron beam is offset to the wafer resulting in the inspection pattern partially being out of the detection image of the secondary electron beam, which could not be handled only with the technology for optimizing a matching region within the detection image. This problem could be a fatal drawback especially in the inspecting of patterns of high precision.
Therefore, a still further object of the present invention is to provide a defect inspection apparatus which can prevent a loss of accuracy in the defect detection possibly caused by a position mismatch between the image of an inspection sample and a reference image.
Another object of the present invention is to provide a semiconductor manufacturing method used in semiconductor device manufacturing processes, which attempts to improve the yield of devices and to prevent any faulty products from being delivered to market by using a defect inspection apparatus as described above for performing a defect detection of a sample.
Means to Solve the Problem
The present invention has employed a method referred to as a projecting method using an electron beam as a means for improving the inspection rate which has been essential drawback of the SEM method. The projecting method will now be described below.
In the projecting method, an observation region on a sample is irradiated in block by a primary electron beam (i.e., no scanning but an irradiation covering a certain area), and secondary electrons emanated from the irradiated region are formed into an image in block by a lens system on a detector (a micro-channel plate plus fluorescent screen) as an image of electron beam. That image is used in a two-dimensional CCD (charge coupled device) or a TDI-CCD (a line image sensor) to convert the image data into an electric signal, which is then output onto a CRT or stored in some storage medium. From this image data, defects in the sample wafer (the semiconductor (Si) wafer being processed) may be detected. In the case of the CCD, the moving direction of the stage extends along the shorter axis (it may be along the longer axis), and the movement is made by the step and repeat manner. As for the stage movement in the case of TDI-CCD, the stage is continuously moved in the accumulation direction. Since the TDI-CCD allows the image to be serially obtained, the TDI-CCD may be used when the defect inspections are to be continuously carried out. The resolution is determined depending on the magnification and accuracy of an image-forming optical system (a secondary optical system), and in an embodiment, a resolution of 0.05 .mu.m has been obtained. In this example, with a resolution of 0.1 .mu.m and the electron beam irradiation condition of 1.6 .mu.A for the area of 200 .mu.m.times.50 .mu.m, an inspection time of about one hour per 20 cm wafer has been accomplished, which is 8 times higher than in the SEM method. The specification of the TDI-CCD employed herein has 2048 pixels.times.512 arrays with a line rate of 3.3 .mu.s (at line frequency of 300 kHz). In this example, although an irradiation area is determined so as to conform to the specification of the TDI-CCD employed, the irradiation area may be changed depending on the object to be irradiated.
Problems in this projecting method are; (1) a charge build-up is more likely to occur in the surface of a sample due to an in-block irradiation of electron beam; and (2) an electron current obtained by this method is limited (up to about 1.6 .mu.A), which prohibits any improvement in inspection rate.
Now, in order to dissolve the above mentioned problems of the conventional techniques, according to 1.sup.st aspect of the present invention, there is provided an inspection apparatus for inspecting an object to be inspected by irradiating either of a charged particles or an electromagnetic waves onto said object, said apparatus comprising:
a working chamber for inspecting said object, said chamber capable of being controlled to be vacuum atmosphere;
a beam generating means for generating either of said charged particles or said electromagnetic waves as a beam;
an electronic optical system for guiding and irradiating said beam onto said object to be inspected held in said working chamber, detecting a secondary charged particles emanated from said object to be inspected and introducing said secondary charged particles to an image processing system;
said image processing system for forming an image by said secondary charged particles;
an information processing system for displaying and/or storing the status information of said object to be inspected based on output from said image processing system; and
a stage unit for operatively holding said object to be inspected so as to be movable with respect to said beam.
According to 2.sup.nd aspect of the present invention, in the inspection apparatus of 1.sup.st aspect, the inspection apparatus further comprises a carrying mechanism for securely accommodating said object to be inspected and for transferring said object to or from said working chamber.
According to 3.sup.rd aspect of the present invention, in the inspection apparatus of 2.sup.nd aspect, said carrying mechanism comprises;
a mini-environment chamber for supplying a clean gas to said object to be inspected to prevent dust from contacting said object to be inspected;
at least two loading chambers disposed between said mini-environment chamber and said working chamber, and adapted to be independently controllable so as to be a vacuum atmosphere; and
a loader having a carrier unit capable of transferring said object to be inspected between said mini-environment chamber and said loading chambers, and another carrier unit capable of transferring said object to be inspected between said one loading chamber and said stage device;
wherein said working chamber and said loading chamber are supported through a vibration isolator.
According to 4.sup.th aspect of the present invention, in the inspection apparatus of 1.sup.st aspect, said inspection apparatus further comprising:
a precharge unit for irradiating a charged particle beam to said object to be inspected placed in said working chamber to reduce variations in charge on said object to be inspected; and
a potential applying mechanism for applying a potential to said object to be inspected.
According to 5.sup.th aspect of the present invention, in the inspection apparatus of 3.sup.rd aspect, said loader includes:
a first loading chamber and a second loading chamber capable of independently controlling an atmosphere therein;
a first carrier unit for carrying said object to be inspected between said first loading chamber and the outside of said first loading chamber; and
a second carrier unit disposed in said second loading chamber for carrying said object to be inspected between said first loading chamber and said stage device.
According to 6.sup.th aspect of the present invention, in the inspection apparatus of 1.sup.st, 2.sup.nd or 3.sup.rd aspect, the inspection apparatus further comprises:
an alignment controller for observing the surface of said object to be inspected for an alignment of said object to be inspected with respect to said electron-optical system to control the alignment; and
a laser interference range finder for detecting coordinates of said object to be inspected on said stage device, said coordinates of said object to be inspected being determined by said alignment controller using patterns formed on said object to be inspected.
According to 7.sup.th aspect of the present invention, in the inspection apparatus of 1.sup.st, 2.sup.nd or 3.sup.rd aspect, the alignment of said object to be inspected includes:
rough alignment performed within said mini-environment space; and
alignment in XY-directions and alignment in a rotating direction performed on said stage device.
According to b 8.sup.th aspect of the present invention, in the inspection apparatus of 1.sup.st, 2.sup.nd or 3.sup.rd aspect, said electron optical system includes:
an E.times.B separator for deflecting said secondary charged particle toward said detector by a field where an electric field and a magnetic field cross at right angles; and an electrode for controlling an electric field intensity in a plane of said sample to be inspected, said plane being exposed to said electron beam irradiation, said electrode being arranged between said objective lens and said sample to be inspected and having a shape approximately symmetrical with respect to the optical axis of irradiation of said beam.
According to 9.sup.th aspect of the present invention, in the inspection apparatus of 1.sup.st, 2.sup.nd or 3.sup.rd aspect, said apparatus includes an E.times.B separator, to which said charged particle and said secondary charged particle are entered, said secondary charged particle being advanced in the direction approximately opposite to said charged particle, and in which said charged particle or said secondary charged particle is deflected selectively, said E.times.B separator characterized in that: an electrode for generating an electric field is made up of three or more pairs of non-magnetic conductive electrodes, and is arranged so as to approximately form a cylinder.
According to 10.sup.th aspect of the present invention, in the inspection apparatus of 1.sup.st, 2.sup.nd or 3.sup.rd aspect, said apparatus further comprises a charged particle irradiating section for irradiating charged particles in advance against said inspecting region just before the inspection.
According to 11.sup.th aspect of the present invention, in the inspection apparatus of 1.sup.st, 2.sup.nd or 3.sup.rd aspect, said apparatus further comprising a means for making the distribution uniform or reducing the potential level of electric charge residing on said object.
According to 12.sup.th aspect of the present invention, in the inspection apparatus of 1.sup.st, 2.sup.nd or 3.sup.rd aspect, electrons having energy lower than that of said charged particles are supplied to said sample at least during said detector detecting said secondary charged particle image.
According to 13.sup.th aspect of the present invention, in the inspection apparatus of 1.sup.st, 2.sup.nd or 3.sup.rd aspect, said stage is an XY stage, which is accommodated in a working chamber and supported by a hydrostatic bearing in a non-contact manner with respect to said working chamber;
said working chamber in which said stage is accommodated is exhausted to vacuum; and
a differential exhausting mechanism is arranged surrounding a portion in said charged particle beam apparatus, where the charged particle beam is to be irradiated against a surface of said sample, so that a region on said sample to which said charged particle beam is to be irradiated may be exhausted to vacuum.
According to 14.sup.th aspect of the present invention, in the inspection apparatus of 1.sup.st, 2.sup.nd or 3.sup.rd aspect, said apparatus includes an apparatus for irradiating a charged particle beam against a surface of a sample loaded on an XY stage while moving said sample to a desired position in a vacuum atmosphere,
said XY stage is provided with a non-contact supporting mechanism by means of a hydrostatic bearing and a vacuum sealing mechanism by means of differential exhausting, and a divider is provided for making the conductance smaller between a charged particle beam irradiating region and a hydrostatic bearing support section, so that there is a pressure difference to be produced between said charged particle beam irradiating region and said hydrostatic bearing support section.
According to 15.sup.th aspect of the present invention, in the inspection apparatus of 1.sup.st, 2.sup.nd or 3.sup.rd aspect, said apparatus includes;
an image obtaining means for obtaining respective images for a plurality of regions to be inspected, said regions being displaced from one another while being partially superimposed one on another on said sample;
a storage means for storing a reference image; and a defect determination means for determining any defects in said sample by comparing said respective images obtained by said image obtaining means for said plurality of regions to be inspected with said reference images stored in said storage means.
According to 16.sup.th aspect of the present invention, there is provided a device manufacturing method, which comprises the step of:
detecting defects on a wafer using an inspection apparatus according to anyone of 1.sup.st to 15.sup.th aspect in the middle of a process or subsequent to the process.
According to 1.sup.st to 16.sup.th aspects of the present invention, the following advantages are provided:
(A) the general configuration can be established for an inspection apparatus in accordance with a charged particle based projection scheme, which can process objects under inspecting at a high throughput;
(B) a clean gas is forced to flow to an object to be inspected within the mini-environment space to prevent dust from attaching to the object to be inspected, and a sensor is provided for observing the cleanliness, thereby making it possible to inspect the object to be inspected while monitoring dust within the space;
(C) when the loading chamber and the working chamber are integrally supported through a vibration isolator, an object to be inspected can be carried to the stage device and inspected thereon without being affected by the external environment; and
(D) when the precharge unit is provided, a wafer made of an insulating material will not be affected by charging.
According to 17.sup.th aspect of the present invention, there is provided an inspection apparatus which comprises:
a beam source for irradiating a charged particle against a sample to be inspected;
a retarding-field type objective lens for decelerating said charged particle as well as for accelerating secondary charged particle generated by said electron beam irradiated against said sample to be inspected;
a detector for detecting said secondary charged particle;
an E.times.B deflecting system for deflecting said secondary charged particle toward said detector by a field where an electric field and a magnetic field cross at right angles; and
an electrode for controlling the electric field intensity in a plane of said sample to be inspected, said plane being exposed to said charged particle irradiation, said electrode being arranged between said retarding-field type objective lens and said sample to be inspected and having a shape approximately symmetrical with respect to an optical axis of irradiation of said charged particles.
According to 18.sup.th aspect of the present invention, in the electron beam apparatus of 17.sup.th aspect, a voltage applied to said electrode is controlled in order to control said electric field intensity depending on a category of said sample to be inspected.
According to 19.sup.th aspect of the present invention, in the electron beam apparatus of 17.sup.th aspect, said sample to be inspected is a semiconductor wafer, and said voltage applied to said electrode in order to control said electric field intensity is controlled depending on whether or not said semiconductor device has a via.
According to 20.sup.th aspect of the present invention, there is provided a device manufacturing method which uses an electron beam apparatus defined by either of 17.sup.th to 19.sup.th aspect, wherein said method is characterized in that a semiconductor wafer, which has been prepared as said sample to be inspected, is inspected for defects by using said inspecting apparatus in a manufacturing process of the device or subsequent to the process.
According to 17.sup.th to 20.sup.th aspect of the present invention, the following advantages are provided.
Since the electrode having a shape approximately symmetrical with respect to the axis of irradiation of the charged particles has been arranged between the sample to be inspected and the objective lens so as to control the electric field intensity in the charged particle irradiated plane of the sample to be inspected, therefore the electric field between the sample to be inspected and the objective lens can be controlled.
Further, since the electrode having a shape approximately symmetrical with respect to the axis of irradiation of the charged particle has been arranged between the sample to be inspected and the objective lens so as to weaken the electric field intensity in the charged particle irradiated plane of the sample to be inspected, therefore the electric discharge between the sample to be inspected and the objective lens can be eliminated.
Since there has been no modification such as decreasing the voltage applied to the objective lens and therefore the secondary charged particles can go through the objective lens efficiently, thus a detection efficiency can be improved and a signal with good S/N ratio can be obtained.
Further, the voltage can be controlled so as to weaken the electric field intensity in the charged particle irradiated plane of the sample to be inspected, depending on the type of sample to be inspected.
For example, if the sample to be inspected is of a type that is likely to cause an electric discharge between the objective lens and itself, the electric discharge can be prevented by weakening the electric field intensity in the charged particle irradiated plane of the sample to be inspected by changing the voltage applied to the electrode.
Further, the voltage applied to the electrode can be changed depending on whether or not said semiconductor device has a via, that is, the voltage applied in order to weaken the electric field intensity in the charged particle irradiated plane of the semiconductor wafer can be changed.
For example, if the sample to be inspected is of a type that is likely to cause an electric discharge between the objective lens and itself, the electric discharge especially in the via or in the vicinity of the via can be prevented by changing the electric field caused by the electrodes and thereby weakening the electric field intensity in the charged particle irradiated plane of the sample to be inspected.
Further, since an electric discharge is prevented between the via and the objective lens, there would be no damage to the pattern or the like in the semiconductor wafer, which otherwise would be caused by the electric discharge.
Further, since the potential applied to the electrode has been made lower than that applied to the sample to be inspected, therefore the electric field intensity in the charged particle irradiated plane of the sample to be inspected can be weakened, thus preventing the electric discharge to the sample to be inspected.
Yet further, since the potential applied to said electrode is negative and the sample to be inspected has been grounded, the electric field intensity is weakened in the charged particle irradiated plane of the sample to be inspected, to prevent an electric discharge to the sample to be inspected.
According to 21.sup.st aspect of the present invention, there is provided an E.times.B separator, into which a first charged particle beam and a second charged particle beam enter, said second charged particles being advanced in the direction approximately opposite to said first charged particle beam, and in which said first charged particle beam or said second charged particle beam is deflected selectively, said E.times.B separator characterized in that:
an electrode for generating an electric field is made up of three or more pairs of non-magnetic conductive electrodes, and is arranged so as to form cylinder.
According to 22.sup.nd aspect of the present invention, in the E.times.B separator of 21.sup.st aspect, each of a pair of parallel plate magnetic poles for generating a magnetic field is respectively arranged outside of said cylinder composed of said three or more pairs of non-magnetic conductive electrodes, and projections are formed in peripheral portions of the opposite face of each of said pair of parallel plate magnetic poles.
According to 23.sup.rd aspect of the present invention, in the E.times.B separator of 22.sup.nd aspect, in a passage space of lines of magnetic force of the magnetic field generated, a majority of the passage space other than that between said parallel plate magnetic poles is formed to be cylindrical shape coaxial with said cylinder composed of said three or more pairs of non-magnetic conductive electrodes.
According to 24.sup.th aspect of the present invention, in the E.times.B separator of 22.sup.nd or 23.sup.rd aspect, said parallel plate magnetic poles are made of permanent magnets.
According to 25.sup.th aspect of the present invention, in the defect inspection apparatus using the E.times.B separator defined by either of 21.sup.st to 24.sup.th aspect, either one of said first charged particle beam or said second charged particle beam is a primary charged particle beam to be irradiated against a sample to be inspected, and the other is a secondary charged particle beam generated from said sample by the irradiation of said primary charged particle beam.
According to 21.sup.st to 25.sup.th aspect of the present invention, the following advantages are provided.
Both of the electric field and the magnetic field are allowed to emerge uniformly in the larger region around the optical axis, so that even if the area exposed to the irradiation of the charged particle is extended, the aberration for the image passed through the E.times.B separator would fall into a reasonable range of values.
Since the projections have been arranged in the peripheral portions of the magnetic poles generating the magnetic field, and said magnetic poles are also arranged outside of the electrodes for generating the electric field, they allow a uniform magnetic field to be generated, reducing a distortion by the magnetic poles. Further, since the magnetic field has been generated by use of the permanent magnets, the E.times.B separator can be fully installed in vacuum. Still further, the electrodes for generating the electric field and the magnetic circuit for forming the magnetic path have been formed into coaxial cylindrical shapes centered to the optical axis, which makes it possible to reduce in size the E.times.B separator as a whole.
According to 26.sup.th aspect of the present invention, there is provided a projective type electron beam inspection apparatus, which comprises a charged particle irradiating section, a lens system, a deflecting system, an E.times.B filter (Wiener filter), and a secondary charged particle detector, in which charged particles from said charged particle irradiating section is irradiated onto an inspecting region of a sample through said lens system, said deflecting system, and said E.times.B filter, and secondary charged particles emitted from the sample are formed into an image in said secondary charged particle detector by said lens system, said deflecting system, and said E.times.B filter, and an electric signal thereof is inspected as the image, said apparatus characterized in further comprising a charged particle irradiating section for irradiating charged particles in advance against said inspecting region just before the inspection.
According to 27.sup.th aspect of the present invention, in the apparatus of 26.sup.th aspect, said charged particle is selected from the group consisting of electron, positive or negative ion, or plasma.
According to 28.sup.th aspect of the present invention, in the apparatus of 26.sup.th or 27.sup.th aspect, the energy of said charged particles is equal to or less than 100 eV.
According to 29.sup.th aspect of the present invention, in the apparatus of 26.sup.th or 27.sup.th aspect, the energy of said charged particles is not greater than 30 eV.
According to 30.sup.th aspect of the present invention, there is provided a device manufacturing method using an inspection apparatus defined by either of 26.sup.th to 29.sup.th aspect, wherein a pattern inspection is performed in the device manufacturing processes.
According to 26.sup.th to 30.sup.th aspect of the present invention, the following advantages are provided.
Since a pre-treatment by means of a charged particle irradiation is employed just before a measurement, an evaluated image distortion by the charging would not occur or could be neglible, therefore all defects can be accurately detected.
Further, since a high current can be used for scanning a stage by such an amount that has caused a problem in the prior art, a large amount of secondary electrons can be detected and a detection signal having a good S/N ratio can be obtained, thus reliability of the defect detection.
Still further, with a larger S/N ratio, faster scanning of the stage can still produce good image data, thus improving inspection throughput.
According to 31.sup.st aspect of the present invention, there is provided an imaging apparatus which irradiates a charged particle beam emitted from a beam source against an object and detects a secondary charged particle emanated from the object by using a detector so as to collect an image data of said object, to inspect the object for defects and so forth,
said apparatus characterized in further comprising a means for making the distribution uniformor reducing the potential level of electric charge residing on said object.
According to 32.sup.nd aspect of the present invention, in the imaging apparatus of 31.sup.st aspect, said means comprises an electrode disposed between said beam source and said object so as to be capable of controlling said electric charge.
According to 33.sup.rd aspect of the present invention, in the imaging apparatus of 3.sup.st aspect, said means is designed so as to operate during the idle time between measurement timings.
According to 34.sup.th aspect of the present invention, in the imaging apparatus of 31.sup.st aspect, said imaging apparatus further comprises:
at least one or more primary optical systems for irradiating a plurality of charged particle beams against said object; and at least one or more secondary optical systems for guiding electrons emanating from said object to at least one or more detectors, wherein
each of said plurality of primary charged particle beams is respectively irradiated onto a spot such that the distance between any two spots is greater than the distance resolution of said secondary optical system.
According to 35.sup.th aspect of the present invention, there is provided a device manufacturing method characterized in that a defect in a wafer is detected in the course of processing by using the imaging apparatus disclosed in either of 31.sup.st to 34.sup.th aspects.
According to the invention of 31.sup.st to 35.sup.th aspects, the following effects may be expected to obtain.
(A) Distortion in an image caused by electric charging may be reduced regardless of the properties of the object to be inspected.
(B) Since the idle time between the timings for the conventional measurement is used to offset the electric charging and make it uniform, there would be no affect on throughput.
(C) Since real-time processing becomes possible, time for any post-processing, a memory and the like are no more necessary.
(D) A fast and highly accurate observation of an image and detection of a defect may be accomplished.
According to 36.sup.th aspect of the present invention, there is provided an inspection apparatus for inspecting a sample for defects, comprising: a charged particle irradiation means capable of irradiating primary charged particles against said sample; a projecting means for projecting secondary charged particles emanating from said sample by the irradiation of said primary charged particles so as to form an image; a detection means for detecting an image formed by said projecting means as an electron image of said sample; and a defect evaluation means for determining a defect in said sample based on an electron image detected by said detection means, said apparatus characterized in that electrons having energy lower than that of said irradiated primary charged particle are supplied to said sample at least during said detection means detecting said electron image.
In the 36.sup.th aspect of the present invention, the charged particle irradiation means irradiates primary charged particles against the sample, and the projecting means projects the secondary charged particle emanating from the sample in response to the irradiation of the primary charged particles so as to form the image in the detection means. The sample, which has emitted out the secondary charged particle therefrom, is charged up to a positive potential. The detection means detects the formed image as the electron image of the sample, and the defect evaluation means determines whether any defects exist in the sample based on the detected electron image. In that case, at least during the time period when the detection means is detecting the electron image, electrons having energy lower than that of the irradiated primary charged particles is supplied to the sample. Those electrons of lower energy may neutralize the sample that has been positively charged-up by an emanation of the secondary charged particle gone from the sample. This allows the secondary charged particle to be formed into an image without any substantial effect from the positive potential of the sample, and thereby the detection means can detect the electron image with the reduced image distortion.
As for electrons having energy lower than that of the primary charged particle, preferably, for example, UV photoelectrons may be used. The UV photoelectron is defined as an electron emanated from a substance such as metal or the like by the photoelectric effect upon irradiation of a beam of light including ultra-violet ray (UV) to said substance. Alternatively, any means other than the charged particle irradiation means, for example, an electron gun or the like may be used to generate electrons having the energy lower than that of the primary charged particle.
It is to be noted that those secondary charged particles which have emanated from the sample by the irradiation of the primary charged particles may include some reflected electrons generated by the primary charged particle which have been reflected from the sample surface in addition to the secondary electrons originated from those electrons which were once in the sample but which have emanated from the surface thereof by the impingement of the primary charged particle thereto. It is apparent that the electron image to be formed by the detection means of the present invention also includes a contribution from those back scattered electrons.
According to 37.sup.th aspect of the present invention, there is provided a defect inspection apparatus for inspecting a sample for any defects, comprising: a charged particle irradiation means capable of irradiating a primary charged particle against said sample; a projecting means for projecting a secondary charged particle emanated from said sample by the irradiation of said primary charged particle so as to form an image; a detection means for detecting an image formed by said projecting means as an electron image of said sample; and a defect evaluation means for determining a defect in said sample based on the electron image detected by said detection means, said apparatus characterized in further comprising a UV photoelectron supply means capable of supplying a UV photoelectron to said sample.
In the 37.sup.th aspect of the present invention, so far as the reduction in image disorder can be accomplished effectively according to the present invention by the UV photoelectron supply means (or in the UV photoelectron supply), the low energy electrons can be supplied to the sample with arbitrary timing and for arbitrary duration. For example, the supply of UV photoelectrons may be started before the primary charged particles are irradiated, before the secondary charged particles are formed into an image, or after the secondary charged particles have been formed into an image but before the electron image is detected. Further, as in the first aspect, the UV photoelectron supply may continue at least while the secondary charged particle is being detected, but the supply of UV photoelectrons may be stopped even before or during the electron image detection if the sample has been electrically neutralized sufficiently.
According to 38.sup.th aspect of the present invention, there is provided a defect inspection method for inspecting a sample for any defects, which comprises: an irradiating process for irradiating primary charged particles against said sample; a projecting process for projecting secondary charged particles emanated from said sample by the irradiation of said primary charged particle so as to form an image; a detecting process for detecting said image formed in said projecting process as an electron image of said sample; and a defect evaluating process for determining a defect in said sample based on said electron image detected in said detecting process, wherein electrons having energy lower than that of said primary charged particles are supplied to said sample at least during said electron image being detected in said detecting process.
According to 39.sup.th aspect of the present invention, there is provided a defect inspection method for inspecting a sample for any defects, which comprises: an irradiating process for irradiating primary charged particles against said sample; a projecting process for projecting secondary charged particles emanated from said sample by the irradiation of said primary charged particles so as to form an image; a detecting process for detecting said image formed in said projecting process as an electron image of said sample; and a defect evaluating process for determining a defect in said sample based on said electron image detected in said detecting process, said method further comprising: a UV photoelectron supplying process for supplying said sample with UV photoelectrons.
According to 40.sup.th aspect of the present invention, there is provided a semiconductor manufacturing method which includes a process for inspecting for any defects a sample to be required in manufacturing a semiconductor device by using a defect inspection apparatus of 36.sup.th or 37.sup.th aspect.
According to the invention of 36.sup.th to 40.sup.th aspects, the following advantages can be expected.
Since electrons having energy lower than that of the primary charged particles are supplied to the sample to be inspected, positive charge-up of the surface of the sample possibly caused by the secondary charged particle emanation may be reduced, and thereby an image distortion of the secondary charged particle resulting from the charging may be also resolved, and the sample may be inspected for defects with high accuracy.
Further, when the defect inspection is conducted by using such a defect inspection apparatus as described above, the yield of the product can be improved and the delivery of defective products can also be prevented.
According to 41.sup.st aspect of the present invention, there is provided an apparatus for irradiating a charged particle beam against the surface of a sample loaded on an XY stage while moving said sample to a desired position in vacuum atmosphere, said apparatus characterized in that:
said XY stage is provided with a non-contact supporting mechanism by means of a hydrostatic bearing and a vacuum sealing mechanism by means of differential exhausting, and
a divider is provided for reducing the conductance between the charged particle beam irradiating region and a hydrostatic bearing support section, so that there is a pressure difference produced between said charged particle beam irradiating region and said hydrostatic bearing support section.
According to 42.sup.nd aspect of the present invention, in the charged particle beam apparatus of 41.sup.st aspect, said divider has a differential exhausting structure integrated therein.
According to 43.sup.rd aspect of the present invention, in the charged particle beam apparatus of 1.sup.st or 42.sup.nd aspect, said divider has a cold trap function.
According to 44.sup.th aspect of the present invention, in the charged particle beam apparatus of either 41.sup.st to 43.sup.rd aspect, said dividers are arranged in two locations including a proximity of the charged particle beam irradiating location and a proximity of the hydrostatic bearing.
According to 45.sup.th aspect of the present invention, in the charged particle beam apparatus either of 41.sup.st to 44.sup.th aspects, the gas supplied to the hydrostatic bearing of said stage is either nitrogen or an inert gas.
According to 46.sup.th aspect of the present invention, in the charged particle beam apparatus either of 41.sup.st to 45.sup.th aspects, a surface treatment is applied to at least the part of the surface facing the hydrostatic bearing in said XY stage so as to reduce the amount of gas to be desorbed.
According to 47.sup.th aspect of the present invention, there is provided a wafer defect inspection apparatus for inspecting a surface of a wafer for defects by using the apparatus disclosed in either of 41.sup.st to 46.sup.th aspects.
According to 48.sup.th aspect of the present invention, there is provided an exposing apparatus for delineating a circuit pattern of a semiconductor device on a surface of a semiconductor wafer or a reticle by using the apparatus disclosed in any of 41.sup.st to 46.sup.th aspects.
According to 49.sup.th aspect of the present invention, there is provided a semiconductor manufacturing method for manufacturing a semiconductor by using the apparatus disclosed in any of 4.sup.st to 48.sup.th aspects.
According to 41.sup.st to 49.sup.th aspect of the present invention, the following effects may be expected to obtain.
(a) The stage device can enhance accurate positioning within vacuum atmosphere, and further, the pressure in the space surrounding the charged particle beam irradiating location is hardly increased. That is, it allows the charged particle beam processing to be applied to the sample with high accuracy.
(b) It is almost impossible for gas desorbed or leaked from the hydrostatic bearing to go though the divider and reach the space for the charged particle beam irradiating system. Thereby, the vacuum level in the space surrounding the charged particle beam irradiating location can be further stabilized.
(c) It is harder for the discharged gas to go through to the space for the charged particle beam irradiating system, and it is easier to maintain the stability of the vacuum level in the space surrounding the charged particles beam irradiating location.
(d) The interior of the vacuum chamber is partitioned into three chambers, i.e., a charged particle beam irradiation chamber, a hydrostatic bearing chamber and an intermediate chamber which communicate with each other via a small conductance. Further, the vacuum exhausting system is constructed to control the pressures in the respective chambers sequentially, so that the pressure in the charged particle beam irradiation chamber is the lowest, the intermediate chamber medium, and the hydrostatic bearing chamber the highest. The pressure fluctuation in the intermediate chamber can be reduced by the divider, and the pressure fluctuation in the charged particle beam irradiation chamber can be further reduced by another step of divider, so that the pressure fluctuation therein can be reduced substantially to a non-problematic level.
(e) The pressure increase upon movement of the stage can be controlled so that it is kept low.
(f) The pressure increase upon movement of the stage can be further controlled to be kept even lower.
(g) Since a defect inspection apparatus with highly accurate stage positioning performance and with a stable vacuum level in the charged particle beam irradiating region can be accomplished, an inspection apparatus with high inspection performance and without any fear of contamination of the sample can be provided.
(h) Since a defect inspection apparatus with highly accurate stage positioning performance and with a stable vacuum level in the charged particle beam irradiating region can be accomplished, an exposing apparatus with high exposing accuracy and without any fear of contamination of the sample can be provided.
(i) Manufacturing the semiconductor by using the apparatus with highly accurate stage positioning performance and with a stable vacuum level in the charged particle beam irradiating region can form a miniaturized micro semiconductor circuit.
According to 50.sup.th aspect of the present invention, there is provided an inspection apparatus or inspection method for inspecting a sample for any defect, which comprises;
an image obtaining means for obtaining respective images for a plurality of regions to be inspected, said regions being displaced from one another while being partially superimposed one on another on said sample;
a storage means for storing a reference image; and
a defect determination means for determining any defects in said sample by comparing said respective images obtained by said image obtaining means for said plurality of regions to be inspected with said reference image stored in said storage means.
According to 51.sup.st aspect of the present invention, in the inspection apparatus or inspection method of 50.sup.th aspect, said apparatus further comprises a charged particle irradiation means for irradiating a primary charged particle beam against each of said plurality of regions to be inspected so that a secondary charged particle beam is emitted from said sample, wherein
said image obtaining means obtains images of said plurality of regions to be inspected in order by detecting said secondary charged particle beam emitted from said plurality of regions to be inspected.
According to 52.sup.nd aspect of the present invention, in the inspection apparatus or inspection method of 51.sup.st aspect, said charged particle irradiation means comprises a particle source for emitting primary charged particles and a deflecting means for deflecting said primary charged particles, wherein
said deflecting means deflects said primary charged particles emitted from said particle source so as to be irradiated against said plurality of regions to be inspected in order.
According to 53.sup.rd aspect of the present invention, in the inspection apparatus or inspection method either of 50.sup.th to 52.sup.nd aspects, said apparatus comprises a primary optical system for irradiating a primary charged particle beam against a sample and a secondary optical system for guiding secondary charged particles to a detector.
According to 54.sup.th aspect of the present invention, there is provided a semiconductor manufacturing method, which includes a process for inspecting a finished or an under processing of wafer for any defect by using an inspection apparatus either of 50.sup.th to 53.sup.rd aspects.
According to 50.sup.th to 54the aspect of the present invention, the following advantages are provided.
Since the defect in the sample can be detected by first obtaining respective images of a plurality of regions to be inspected, which are displaced from one another while being partially superimposed one on another on the sample, and comparing those images of the regions to be inspected with the reference image, any deterioration in the accuracy in the defect detection can be prevented.
Further, according to the device manufacturing method of the invention, since the defect detection is performed by using such a defect inspection apparatus as described above, the yield of the products can be improved and the delivery of any faulty products can be prevented.
According to 55.sup.th aspect of the present invention, there is provided an apparatus for irradiating a charged particle beam against a sample loaded on an XY stage, said apparatus characterized in that: said XY stage is accommodated in a housing and supported by a hydrostatic bearing in a non-contact manner with respect to said housing; said housing in which said stage is accommodated is exhausted to vacuum; and a differential exhausting mechanism is arranged surrounding a portion in said charged particle beam apparatus, where the charged particle beam is to be irradiated against a surface of said sample, so that a region on said sample to which said charged particle beam is to be irradiated may be exhausted to vacuum.
According to this invention, a high-pressure gas supplied for the hydrostatic bearing and leaking into the vacuum chamber is primarily evacuated by a vacuum exhausting pipe connected to the vacuum chamber. Further, arranging the differential exhausting mechanism, which functions to exhaust the region to which the charged particle beam is to be irradiated, so as to surround the portion on which the charged particle beam is to be irradiated, allows the pressure in the irradiation region of the charged particles beam to be decreased to a significantly lower level than that in the vacuum chamber, thus achieving a stable vacuum level where the processing of the sample by the charged particle beam can be performed without any problems. That is to say, a stage with a structure similar to that of a stage of hydrostatic bearing type commonly used in the atmospheric pressure (a stage supported by the hydrostatic bearing having no differential exhausting mechanism) may be used to stably process the sample on the stage by the charged particle beam.
According to 56.sup.th aspect of the present invention, in the charged particles beam apparatus of 55.sup.th aspect, a gas to be supplied to said hydrostatic bearing of said XY stage is nitrogen or an inert gas, and said nitrogen or inert gas is pressurized after having been exhausted from said housing containing said stage so as to be supplied again to said hydrostatic bearing.
According to this invention, since the residual gas components in the vacuum housing are inert, there should be no fear that the surface of the sample or any surfaces of the structures within the vacuum chamber defined by the housing would be contaminated by water contents or oil and fat contents, and in addition, even if inert gas molecules are adsorbed onto the sample surface, once being exposed to the differential exhausting mechanism or the high vacuum section of the irradiation region of the charged particles beam, said inert gas molecules would be released immediately from the sample surface, so that the effect on the vacuum level in the irradiation region of the charged particle beam can be minimized and the processing applied by the charged particle beam to the sample can be stabilized.
According to 57.sup.th aspect of the present invention, there is provided a wafer defect inspection apparatus for inspecting a surface of a semiconductor wafer for defects by using the apparatus of 55.sup.th or 56.sup.th aspect.
This allows the provision of an inspection apparatus which accomplishes positioning performance of the stage with high precision and also provides a stable vacuum level in the irradiation region of the charged particles beam at low cost.
According to 58.sup.th aspect of the present invention, there is provided an exposing apparatus for delineating a circuit pattern of a semiconductor device on the surface of a semiconductor wafer or a reticle by using the apparatus of 55.sup.th or 56.sup.th aspect.
This allows the provision of an exposing apparatus which accomplishes positioning performance of the stage with high precision and also provides a stable vacuum level in the irradiation region of the charged particles beam at low cost.
According to 59.sup.th aspect of the present invention, there is provided a semiconductor manufacturing method for manufacturing a semiconductor by using the apparatus of either of 55.sup.th to 58.sup.th aspects.
This allows a micro semiconductor circuit to be formed by way of manufacturing a semiconductor with the apparatus which accomplishes positioning performance of the stage with high precision and also provides a stable vacuum level in the irradiation region of the charged particles beam.
According to the inventions of 55.sup.th to 59.sup.th aspects, the following effects may be expected to obtain.
(A) Processing by the charged particle beam can be stably applied to a sample on a stage by the use of the stage having a structure similar to that of a stage of hydrostatic bearing type which is typically used at atmospheric pressure (a stage supported by the hydrostatic bearing having no differential exhausting mechanism).
(B) The effect on the vacuum level in the charged particle beam irradiation region can be minimized, and thereby the processing by the charged particle beam to the sample can be stabilized.
(C) Such an inspection apparatus can be provided at low cost that accomplishes positioning performance of the stage with high precision and provides a stable vacuum level in the irradiation region of the charged particle beam.
(D) Such an exposing apparatus can be provided in low cost that accomplishes positioning performance of the stage with high precision and provides a stable vacuum level in the irradiation region of the charged particle beam.
(E) A micro semiconductor circuit can be formed by manufacturing the semiconductor using an apparatus which accomplishes positioning performance of the stage with high precision and provides a stable vacuum level in the irradiation region of the charged particle beam.
According to 60.sup.th aspect of the present invention, there is provided an inspection method for inspecting an object to be inspected by irradiating either of charged particles or electromagnetic waves onto said object to be inspected by using an apparatus which comprises:
a working chamber for inspecting said object to be inspected, said chamber capable of being controlled to be vacuum atmosphere;
a beam source for emitting either of said charged particle or said electromagnetic waves as a beam;
an electronic optical system for guiding and irradiating said beam onto said object to be inspected held in said working chamber, detecting a secondary charged particles emanated from said object to be inspected and introducing said secondary charged particles to an image processing system;
said image processing system for forming an image by said secondary charged particle;
an information processing system for displaying and/or storing status information of said object to be inspected based on an output from said image processing system; and
a stage unit for operatively holding said object to be inspected so as to be movable with respect to said beam,
wherein said method comprises the steps of:
positioning said beam accurately onto said object to be inspected by measuring the position of said object to be inspected;
deflecting said beam onto a desired position of said measured object to be inspected;
irradiating said desired position on a surface of said object to be inspected by said beam;
detecting a secondary charged particle emanating from said object to be inspected;
forming an image by said secondary charged particles; and
displaying and/or storing status information of said object to be inspected based on output from said image processing system.